Analysis of Oligocene
Frio Formation intraslope growth-faulted subbasins in the Corpus Christi,
Texas, area indicates that deposition during relative lowstands of sea
level was the main cause growth faulting. Lowstand depocenters on the
low-gradient upper continental slope comprising basin-floor and slope-fan
systems, and prograding lowstand delta systems exerted sufficient gravity
stress to cause major sections of outer shelf and upper slope strata to
fail and move basinward. The faults sole out deep in the basin. Footwall
block rotation mobilizes deep-water sediments and forces distal mud bodies
basinward and upward to form mud (shale) ridges that constitute the basinward
flank of intraslope subbasins.

Sedimentation associated
with third-order relative falls of sea level generated a major regional
syndepositional growth-fault system. Subbasins on the downthrown side
of each arcuate fault segment that comprises a regional fault system are
filled during the lowstands of sea level. Consequently, genetically similar
but diachronous lowstand depositional systems filled each subsequent growth-faulted
subbasin trend. The subbasin stratigraphy becomes younger basinward because
the subbasin development and fill process extended the Frio shelf edge
stepwise into the Oligocene Gulf of Mexico basin, coinciding with relative
third-order sea-level cycles.

The subbasins, prolific
petroleum targets for decades, are now the focus of prospecting for deep
gas. Lowstand sandstones are principal reservoirs, and synsedimentary
tectonics produced anticlinal fault traps and associated stratigraphic
pinchout traps on the flanks of the structures. Understanding the origin
of the faulted subbasins and their chronostratigraphic relationships and
depositional processes provides a perspective that can improve deep gas
exploration.